Dispersion of the Exciton Polariton Branches in CuCl and Their k‐Dependent Splitting in a Magnetic Field

Abstract

The method of three-photon difference-frequency generation is used to measure resonances on the lower polariton branch in CuC1. Due to the small linewidth of the resonances (smallest width 80 FeVj it is possible to determine the splitting of the lower branch in a magnetic field at different k-values for the first time. Resonances on the upper polariton branches and on the longitudinal exciton branches can also be excited with the use of two-and three-photon sum-frequency generation and two-photon absorption. The rather peculiar wavevector-dependent splitting of the lower polariton branch is explained quantitatively by taking into account the field induced mixing of the Z,-and Zl, ,-excitons.Mit Hilfe der Dreiphotonen-Differenzfrequenzerzeugung konnen Resonanzen auf dem unteren Polaritonast in CuCl angeregt werden. Aufgrund der geringen Linienbreite der Resonanzen (kleinste Breite 80 peV) kann erstmals die k-abhingige Magnetfeldaufspaltung des unteren Astes gemessen werden. Mittels der Zwei-und Dreiphotonen-Summenfrequenzerzeugung und der Zweiphotonenabsorption konnen aul3erdem sowohl Resonanzen auf den oberen Polaritonasten als auch die longitudinalen Exzitonen angeregt werden. Die wellenzahlabhangige Aufspaltung des unteren Polaritonastes wird quantitativ durch die Beriicksichtigung der feldinduzierten Mischung der Z,-und Z,, ,-Exzitonen erkliirt.

Effects of the isotopic composition on the fundamental gap of CuCl

“…24 The short-range exchange interaction leads to a splitting of the Z 3 exciton into ortho-and paraexcitons having ⌫ 5 ͑threefold degenerate͒ and ⌫ 2 ͑nondegenerate͒ symmetry, respectively. 33 Optical transitions to orthoexcitons are onephoton allowed, while to first order the paraexciton is onephoton forbidden. The long-range exchange interaction splits the ⌫ 5 states into transverse and longitudinal orthoexcitons.…”

“…Nonlinear spectroscopy is established as a precise method to investigate these photon-exciton coupled states in wide-band-gap semiconductors. 33 Two-photon absorption ͑TPA͒ can be used to determine the energies of the lowest longitudinal 1s exciton ͑LE1͒ around 3208 meV ͑see Fig. 2͒ and the middle transverse polariton branch ͑TP2͒ around 3216.5 meV.…”

Nanocrystal growth in alkali halides observed by exciton spectroscopy

“…The height of the Z 3 exciton is fitted to the experimental data, and the relative height of the two peaks and the energy difference of the peak maxima are taken from the experimental results in single crystals. 20 The peaks are shaped by assuming a size distribution of nanocrystals following the theory of Lifshitz-Slyozov-Wagner ͑LSW theory͒ ͑Refs. 21 and 22͒ and by using Eq.…”

Nonlinear Spectroscopy in Semiconductors

“…The resonances on the lower polariton branch TP1 can only be obtained by three-photon difference generation as is discussed in detail in [20]. Since most of the resonances of CuCl are very narrow (DE % 0.1 meV) in nonlinear spectroscopy, their splitting in a magnetic field [21], in an electric field [22] and under uniaxial stress [17] can be studied with great accuracy. A lot of information on electronic parameters can be gained by doing k-space spectroscopy in external fields [14].…”

“…A lot of information on electronic parameters can be gained by doing k-space spectroscopy in external fields [14]. As discussed in detail in [21] there is a k-dependent splitting of the upper and lower polariton branch in CuCl in a magnetic field, which even changes sign on the lower branch. …”